Sierra

Avoid "Sierras" when the topic is the vast California mountain range. An online camping guide says, "Translating from Spanish, sierra is plural in itself." A conservation organization elaborates: "The Sierra Nevada is a single, distinct unit, both geographically and topographically, and is well described by una sierra nevada. Strictly speaking, therefore, we should never pluralize the name—such as Sierras, or Sierra Nevadas, or even High Sierras."